In Layer 3 (L3) routing protocols such as, for example, Internal Gateway Protocols (IGPs) and External Gateway Protocols (EGPs), routers share network topology information with other routers in a network utilizing routing update messages that are sent when a topology change is detected. In the steady state the routing tables in all of the routers of the network are consistent. The time required to share information between all routers in a network and bring the route tables to a consistent state is called the convergence time.
These protocols are resilient in the sense that if there is topology change in the network then the network can re-converge to a new steady state. The time required to reach a new network convergence is called the re-convergence time. For networks having redundant paths between all nodes, the removal of a node will cause the network to re-converge to a state where traffic previously forwarded through the removed node will be forwarded utilizing alternate routes. During the re-convergence time the packets that were to have been forwarded through the removed node are dropped.
Resiliency is also a property of some Layer 2 (L2) protocols such as the Spanning Tree Protocol (STP) and some first hop protocols such as the Hot Standby Router Protocol (HSRP) and the Gateway Load Balancing Protocol (GLBP).
There are also dependencies between different protocols running on a network device. Thus, a delay in the reconvergence of one protocol can cause delays in the reconvergence of its dependant protocols. Furthermore, bringing down protocols in a specific order can impact the amount of time required for an overall reconvergence of all protocols running on the device.